Ac Unit Running Backwards . Click to see full answer beside this, can a ac compressor run backwards? Dc, single phase ac and 3 phase ac. Outside A/C condenser fan running backwards? from www.doityourself.com Similar to problem #2, not having enough refrigerant will also cause your air conditioner to constantly run, leading to it overheat. It was spinning the pump backwards. Clean your outside unit using a special coil cleaning spray.